The invention relates generally to the spraying of a substance onto a surface. More specifically, the invention is a plasma transferred wire arc system, apparatus, and method for monitored thermal spraying (collectively, the “system”).
A. Plasma
There are four “states of matter” in physics. Matter can take the form of: (1) a solid; (2) a liquid; (3) a gas; or (4) a plasma. Plasma is an ionized gas consisting of positive ions and free electrons in equal proportions resulting in essentially no overall electric charge. Like a gas, plasma does not have a definitive shape or volume. It will expand to fill the space available to it. Unlike gases, plasmas are electrically conductive. Plasma conducts electricity, produces magnetic fields, and responds to electromagnetic forces. In plasma, positively charged nuclei travel in a space filled of freely moving disassociated electrons. These freely moving electrons allow matter in a plasma state to conduct electricity.
Although the term “plasma” is not commonly used outside the context of science and engineering, there are many common examples of plasma that people encounter in everyday life. Lightning, electric sparks, fluorescent lights, neon lights, and plasma televisions are all examples of plasma. Gas is typically converted into a state of plasma through heat (e.g. high temperatures) or electricity (e.g. a high voltage difference between two points).
B. Thermal Spraying
Thermal spraying is a process by which material is sprayed onto a surface with the purpose of improving the surface that is being sprayed. There are many different types of thermal spraying, including, but not limited to: plasma spraying; detonation spraying; wire arc spraying; plasma transferred wire arc spraying; flame spraying; high velocity oxy-fuel coating spraying (“HVOF”); warm spraying; and cold spraying.
Two of these thermal spraying techniques involve the use of plasma, plasma spraying and plasma transferred wire arc spraying. Plasma spraying involves the introduction of feedstock, which can be in the form of a powder, a liquid, a ceramic feedstock that is dispersed in a liquid suspension, or a wire that is introduced into a plasma jet created by a plasma torch. Plasma transferred wire arc (“PTWA”) spraying is plasma spraying when the feedstock is electrically part of the circuit and is in the form of a wire.
C. PTWA
PTWA can be used to enhance the surface properties of components. Treated components can be protected against extreme heat, abrasion, corrosion, erosion, abrasive wear, and other environmental and operational conditions that would otherwise limit the lifespan and effectiveness of the treated component. Overall durability is enhanced, while at the same time PTWA can also be used to achieve the following advantages with respect to treated components: (1) reductions in weight; (2) cost savings; (3) reduction in friction; (4) and a reduction of stress. In the context of vehicles such as automobiles, PTWA treatment of engine components such as cylinder bores can result in increased fuel economy and lower emissions. PTWA can also be useful in refurbishing old parts as well as in enhancing new parts.
The inputs of a PTWA system are electricity, gas, and consumable feedstock. The output of a PTWA system is a plasma arc between a cathode and an anode, where the anode is an open end of a consumable wire. The plasma spray is what enhances the surface properties of a component or surface being treated. Feedstock in a PTWA system is delivered to the plasma torch in the form of the wire. Electric current travels through the wire as the free end of the wire is moved to where the generated plasma exits the nozzle of the plasma torch. In many PTWA systems, the torch assembly revolves around a longitudinal axis of the wire feedstock while maintaining an electrical connection, a plasma arc, between the cathode of the plasma torch and the open end of the wire feedstock. In some embodiments, there is an offset between the longitudinal axis of the wire feedstock and the center of revolution (from the perspective of a cathode revolving around a center point) or the center of rotation (from the perspective of a cathode and surrounding empty space rotating around a center point). See U.S. Pat. No. 8,581,138 which discloses a thermal spray technology “wherein the method includes the steps of offsetting the central axis of a consumable wire with respect to an axial centerline of a constricting orifice.”
PTWA can provide highly desirable benefits in the treatment of components used in a wide variety of different industries, including but not limited to: aerospace; automotive; commercial vehicles; heavy industrial equipment; and rail.
D. Operating Parameters
The correct functioning of a PTWA system typically requires the coordination of: (1) a straight and rapidly traveling feed wire between about 100-500 inches/minute; (2) stable current traveling through the rapidly traveling feed wire; and (3) a consistent gas flow/pressure sufficient for sustaining stable plasma temperatures typically between 6,000 and 20,000 degrees Celsius. If one or more of the parameters of a PTWA system fall outside the desired ranges, inconsistent melting of the feed wire can result. Such inconsistency can negate the desired advantages of PTWA spraying. In extreme cases, such inconsistencies can result in a waste of the feedstock and the component being sprayed.
The correct functioning of a PTWA system requires the coordination of different variables under substantially tight constraints. Operations outside those constraints are not necessarily visible to the human eye unless the undesirable effects are severe. For example, a PTWA system functioning outside of desired parameters can result in “spitting” because the system will project large molten globules instead of finely atomized particles onto the surface being treated by the PTWA system. Even before visible “spitting” occurs, the operation of a PTWA system with even one parameter outside of an acceptable range can be highly undesirable.
E. Monitoring Patterns in the Data
Prior art PTWA systems may monitor certain parameters such as voltage measurements in the electrical pathway that are used to sustain a plasma arc. However, prior art PTWA systems do not analyze data for patterns in the data collected over time, i.e. process the data captured over time as waveforms. The failure to process a series of data as a waveform means that such systems can experience undesirable performance degradations that are not noticed by human operators until after the fact.
The prior art misses some valuable opportunities to proactively identify undesirable operating conditions before such conditions result in undesirable outcomes because the prior art fails to look for patterns in the sensor data. Prior art approaches do not process at least some of the sensor data as a waveform.
The system can be further understood as described in the Summary of the Invention section set forth below.